Lyon, 33, posted a 3.10 ERA in 67 appearances split between the Astros and Blue Jays last season, striking out 63 and walking 20 in 61 innings. He was the primary closer for the D-backs in 2008 and the Astros from 2010-11, before surgery to his right shoulder and biceps tendon derailed his career in '11.

With the Mets, Lyon figures to slide into a setup role alongside Bobby Parnell, though he could also step in as at least a part-time closer. Manager Terry Collins told the New York Post on Wednesday that the ninth-inning job still belongs to Frank Francisco, but general manager Sandy Alderson was not nearly so strong in his words earlier this week.

"I think a lot will depend on what we see over the course of February and March," the GM said.

Alderson also said that he is done adding roster pieces after Lyon, with the possible exception of free-agent outfielder Michael Bourn. That deal is unlikely to come to fruition unless Major League Baseball rules that the Mets could keep their 2013 first-round Draft pick, which they would currently have to forfeit in order to sign Bourn.

As far as the bullpen, the Mets have more than a dozen legitimate contenders for seven Opening Day spots, though veterans Scott Atchison, LaTroy Hawkins and Pedro Feliciano are all strong bets to make the team.

Lyon, who received the second big league contract the Mets handed out this winter, is a lock to make the roster, as are Parnell and -- assuming he is healthy -- Francisco. Lefty Josh Edgin is also a prime candidate to break camp with the Mets.

This marks the second straight winter the Mets made significant changes to their bullpen. Last year's makeover, which centered around Francisco, Jon Rauch and Ramon Ramirez, did not work -- the Mets finished 29th in the league in bullpen ERA. Rauch and Ramirez recently signed contracts with the Marlins and Giants, respectively.

Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDicomo. This story was not subject to the approval of Major League Baseball or its clubs.